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Hemoglobin is a protein found in red blood cells that carries oxygen from the lungs to all parts of the body and returns carbon dioxide back to the lungs. Testing hemoglobin levels is one of the most common laboratory tests performed as part of a complete blood count. This test helps healthcare providers evaluate overall health and diagnose various medical conditions including anemia, polycythemia, and other blood disorders.

Normal hemoglobin levels vary depending on age and sex. For adult men, normal values typically range from 13.5 to 17.5 grams per deciliter of blood, while for adult women the range is usually 12.0 to 15.5 grams per deciliter. Children and pregnant women have different reference ranges. Low hemoglobin levels indicate anemia, which can result from iron deficiency, vitamin deficiencies, chronic diseases, blood loss, or bone marrow problems. Symptoms of low hemoglobin include fatigue, weakness, pale skin, shortness of breath, dizziness, and cold hands and feet.

High hemoglobin levels, though less common than low levels, can also indicate health problems. Elevated hemoglobin may occur in people living at high altitudes, smokers, or those with dehydration. It can also signal conditions such as polycythemia vera, lung disease, heart disease, or kidney tumors. High hemoglobin makes blood thicker, which can increase the risk of blood clots, stroke, and heart attack.

The hemoglobin test is performed using a blood sample, typically drawn from a vein in the arm. No special preparation is usually required, though your healthcare provider may ask you to fast if other tests are being performed simultaneously. The test is quick and results are generally available within hours to a day. If your hemoglobin levels are abnormal, your healthcare provider may order additional tests to determine the underlying cause and recommend appropriate treatment, which might include dietary changes, supplements, medications, or treatment of underlying conditions.